Experimental X-ray Charge Density Studies on the Binary Carbonyls Cr(CO)₆, Fe(CO)₅, and Ni(CO)₄

Abstract

The experimental charge densities in the binary carbonyls Cr(CO)(6) (1), Fe(CO)(5) (2), and Ni(CO)(4) (3) have been investigated on the basis of high-resolution X-ray diffraction data collected at 100 K. The nature of the metal-ligand interactions has been studied by means of deformation densities and by topological analyses using the Atoms in Molecules (AIM) approach of Bader. A detailed comparison between the experimental results and theoretical results from previous work and from gas-phase and periodic DFT/B3LYP calculations shows excellent agreement, both on a qualitative and quantitative level. An examination of the kappa-restricted multipole model (KRMM) for Cr(CO)(6), using theoretically derived structure factors, showed it to provide a somewhat worse fit than a model with freely refined kappa' values. The experimental atomic graphs for the metal atoms in 2 and 3 were found to be dependent on the multipole model used for that atom. In the case of compound 2, restriction of the multipole populations according to idealized site symmetry of D(3h) gave an atomic graph in essential agreement with the theoretical gas-phase study. For compound 3, all multipole models fail to reproduce the atomic graph obtained from the theoretical gas-phase study. The atomic quadrupole moments for the C atoms in all compounds were consistent with significant pi back-donation from the metal atoms.

NATURE OF Mδ+···δ+C-Oδ-INTERACTIONS IN METAL CARBONYLS. AN ELECTRONIC STUDY BASED ON THE TOPOLOGY OF THE ELECTRON CHARGE DENSITY DISTRIBUTION AND ITS LAPLACIAN FUNCTION

“…Las geometrías de todos los monómeros y complejos fueron optimizados sin ninguna restricción con el paquete de programas Gaussian 03, 35 utilizando el funcional híbrido B3LYP, 36 el cual ha demostrado ser adecuado para el tratamiento teórico de sistemas similares, 7,12,37 con el conjunto de funciones bases 6-311++G(2d,2p). De acuerdo a la teoría del campo del ligando, 38 la molécula de CO es un ligando de campo alto, en consecuencia se espera que cuando la coordinación es completa el estado fundamental sea un singulete de capa cerrada.…”

“…Las distancias de enlace M-C y C-O calculadas están en buen acuerdo con las distancias experimentales y teóricas informadas por otros autores. 7,37,[42][43][44] De acuerdo a Orpen y col. 45 la longitud promedio de los enlaces V-C, Cr-C, Mn-C y Fe-C en carbonilos metálicos son 1,946, 1,866, 1,808, y 1,782 Å, respectivamente. Como era de esperar, estas longitudes disminuyen al aumentar el número atómico del metal, debido a que en este sentido disminuye el radio iónico de los metales de transición.…”

Topology of the Spin-Polarized Charge Density in bcc and fcc Iron

“…Other studies have used bond path properties to offer first principles explanations of stress-induced failure in brittle and ductile alloys [7], as well as shear elastic constants in a variety of pure metals and alloys [8][9][10]. Building on these ideas and using the rigorous definitions of bond paths afforded by the theory, the anomalous behavior of iridium under shear was also explained [11].One of the attractive features of AIM is its reliance on the charge density, a quantum mechanical observable, that is most often calculated but can, in principle, be measured via X-ray diffraction techniques [12][13][14][15]. In a similar fashion, the spin-polarized charge density is an observable that can be calculated or measured using spinpolarized neutron diffraction.…”

Bonding in molecular crystals from the local electronic pressure viewpoint

“…We used the experimental electron density and its derivatives expressed in terms of Hansen-Coppens space-extended multipole structural model [80]; in computations, the actual values of these quantities at each point r have been employed. Numerical multipole parameters for benzene, formamide and chromium hexacarbonyl are taken from [81], [82] and [83], correspondingly. The core and valence radial functions of the multipole model are approximated by the atomic wavefunctions listed in [84].…”